Brushless Direct Current (DC) motors are used in a variety of applications including disc drives, compact disc players, digital video disc players, scanners, printers, plotters, actuators used in the automotive and aviation industries, etc. Typically, multiple phase motors include a stationary portion or stator that produces a rotating magnetic field and a non-stationary portion or rotor in which torque is created by the rotating magnetic field. The torque causes the rotor to rotate which in turn causes a shaft connected to the rotor to rotate. At start-up it is desirable to detect the position and rotation rate of the brushless DC motor's rotor. In a brushless DC motor having sensors, the rotor position and its rotation rate may be detected and controlled using Hall sensors. However, the accuracy of Hall sensors is influenced by their operating environment, which decreases the accuracy of the measurements they provide. In sensorless brushless DC motors, the position of the rotor is detected using a Back ElectroMotive Force (BEMF) signal. A drawback with using a BEMF signal is that it becomes very small when the rotor is moving slowly or not at all.
Accordingly, it would be advantageous to have a method for starting a brushless sensorless DC motor using a BEMF signal. It would be of further advantage for the method to be cost efficient to implement.